Tension control system



March 12, 1940. E. P. CODLING ,193,121

TENSION CONTROL SYSTEM Filed Aug. 1:, 1938 2 Sheets-Sheet 2 WITNESSES:

INVENTOR I flared/Pam BY 14 9 7 M6. W

ATTORNEY Patented Mar. 12, 1940 UNITED STATES PATENT OFFICE TENSIONCONTROL SYSTEM Vania Application August 13,

10 Claims.

My invention relates to control systems and it has particular relationto a system for controlling the tension of a material as it is unwoundfrom a reel.

When a strand, a web, or material in other forms, is unwound from a reelthe tension of the material may be maintained by braking means appliedto the reel. The tension of the material varies because of the change inspeed of the reel which results from the change in effective radius ofthe reel. This may be more clearly explained by the equation for powerdeveloped which is (1) Power torque speed in R. P. M.

The required torque is,

(2) Torque=tension effective radius and,

Linear speed (of material) (3) Speed m 0: Effective radius Therefore thepower required is proportional to Linear speeL Tension effective radiusXm Power tension linear speed If the linear speed of the material ismaintained constant, then Power tension system for maintainingsubstantially constant tension in a material as it passes from a supplyreel.

A further object of my invention is to provide tension developing meansthat shall be operable to maintain substantially constant tension inmaterial as it is unwound from a. supply reel.

A more specific object of my invention is to provide for maintainingsubstantially constant tension in a material as it is passed from asupply reel at a constant linear velocity.

1938, Serial No. 224,722

An ancillary object of my invention is to provide for maintainingsubstantially constant tension in a plurality of strands as they arecombined to form a cable.

While my invention will be explained in reference to a system formaintaining constant tension in a. strand such as a wire or a cable, itwill readily be understood that it may be utilized for maintaining aconstant tension in a web, or in any other application where a constantload or braking effect at variable speed is required.

According to a preferred embodiment of my invention, a strand isadvanced from a reel at a constant linear velocity. To maintain constanttension, a dynamo-electric machine or electric brake is mechanicallyconnected to the reel. The electric brake comprises a squirrel-cagerotor winding and a stator winding energized by a constantunidirectional current. As hereinbefore explained, the power developedby the braking means must be constant to maintain constant tension. Theessential characteristics of the electric brake may best be understoodby explaining why the power developed by the brake remains constant whenthe speed is varied.

The current I in the squirrel-cage winding of the electric brake may beexpressed as ing. R is the resistance and X is the inductive reactanceof the squirrel-cage winding.

where 701 is a constant.

If it is assumed that the resistance component R of the impedance Z isnegligible compared with the inductive reactance .X, then,

Z=X=21rfL (approx) 1 where f is the frequency and L is the inductance ofthe squirrel-cage winding. Since L is constant for a particular machineand f is proportional to the speed, then Z=k2 X speed where kg is aconstant and in X speed I sPeedconstant Power developed by the electricbrake is equal to PR, and since I is constant, power and thus tensionwill be constant when operating at variable speed.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself; however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments, when read in connection with the accompanying drawings, inwhich:

Figure 1 is a diagrammatic view of a control system organized inaccordance with the present invention;

Fig. 2 is a partial view in section showing a rotor slot and conductor;

Figs. 3 and 4 illustrate graphically the operation of the arrangementshown in Fig. 1; and

Fig. 5 is a diagrammatic view of a modification of my invention.

Referring more particularly to Fig. 1 of the drawings, referencecharacter II represents a tension control unit comprising a roll or reelI3 upon which a strand I5 or any other material is carried. The strandI5 is advanced from the reel I3 at a constant linear speed by anysuitable means well known in the art, such as a capstan I1.

In order to maintain the tension of the strand I5 substantiallyconstant, a dynamoelectric machine or electric brake I9 is mechanicallyconnected to and driven by the reel I3. The electric brake may bedirectly coupled to the reel or it may be driven by means of a belt 2|as shown in the drawing. The electric brake I9 comprises a. stator 23having a plurality of salient poles 25 and field windings 21, and arotor 29 having a squirrel-cage winding 3|. The winding 3| is of a typehaving a high reactance, that is, the inductive reactance of the windingis high compared to the resistance. To obtain a high reactance eachsemi-closed slot 33 on the rotor 29 may be made substantially as shownin Fig. 2.

During the starting and the stopping of the movement of the strand I5from reel I3, the linear speed will tend to vary, thus normally varyingthe tension of the strand I5. Furthermore, when the reel I3, and thusthe rotor 29, is at rest, the electric brake I9 will produce no brakingeffect to maintain tension in the strand I5. Therefore, a torque motor35 or any other suitable torque producing means is also mechanicallyconnected to the reel I3 to maintain tension in the strand I5.

To obtain a more compact unit, the electric brake I9 and the torquemotor 35 may be assmbled in a common frame. Furthermore, since it willreadily be understood that the electric brake may have non-salient polesinstead of the salient poles 25, the stator winding of the torque motor35 and the field windings 21 of the electric brake may be wound on thesame stator, or one stator winding may be utilized to serve at alternateintervals as the stator winding of the torque motor and as the fieldwinding of the electric brake. In either case, only one rotor windingwill be required.

An electromagnetiodevice 31 having an operating coil 39 and a pluralityof contact members H, 43, 45, 41 and 49 is utilized to control theenergization of the field windings 21 and the torque motor 35. The fieldwindings 21 are connected to a constant potential source ofunidirectional current (not shown) by means of contact members H and 43through conductors 5| and 53. The torque motor 35 is connected to asuitable source of alternating current (not shown) by means of contactmembers 45, 41 and 49 through conductors 55, 51 and 59.

A centrifugally-operated device GI is mechanically connected to the reeland disposed to be actuated at a predetermined speed of the reel I3 toenergize the operating coil 39.

To place the system shown in Fig. 1 in operation, a multi-contact switch63 is closed thereby energizing the torque motor 35 to apply a constanttorque as indicated by curve 65, Fig. 3, to the reel I3. The capstan I1is accelerated until the strand I5 reaches a predetermined linear speed.When the reel I3 reaches a predetermined speed in R. P. M., thecentrifugal device 6| is actuated thus energizing operating coil 39.Preferably, but not necessarily, the contact members 4| and 43 aredisposed to be closed substantially simultaneously with the opening ofcontact members 45, 41 and 49 when electromagnetic device 31 is actuatedby the energizertion of operating coil 39. The torque motor 35 is thusdeenergized and the field windings 21 of electric brake I9 areenergized. As the strand I5 advances from the reel I3, therebydecreasing the effective radius of the reel I3, the rotational speed ofthe reel I3 and the rotor 3I of the electric brake I9 are increased. Thetension of the strand I5 is maintained substantially constant because,as was hereinabove explained, the power developed by the electric brakeI9 remains substantially constant as the speed of the reel is increased.

Curve 61 (Fig. 3) shows, generally, how the torque of the electric brakeI9 varies in relation to the speed in R. P. M. Curves 69 and IIrepresent the iron loss torque and the friction loss torque,respectively, of the electric brake I9. Because of the iron loss and thefriction loss the tension of the strand I5 increases slightly as therotational speed increases when the linear speed of the strand isconstant and only the electric brake I9 is utilized for maintainingtension. This is illustrated by a curve I3 in Fig. 4. In comparison, acurve I5 shows how the tension would vary if only the torque motor 35were utilized for maintaining tension.

In the manufacture of electric cables, especially such as are used inthe communication arts, it is generally desirable to maintain thedistributive capacity of the cable constant. This may be accomplished bymaintaining the tension of the individual strands constant when thestrands are combined to form a cable.

In Fig. 5, a plurality of strand supplies such as the tension controlunits I I described with reference to Fig. 1 are mounted in a twistingunit 8I. The twisting unit 8| is mounted in bearings 83 and 85 to berotatable about its axis. To intertwist the strands at a uniform pitch,the ratio of the linear speed of advance of the strand to the rotationalspeed of the twisting unit is maintained constant. This may beaccomplished by utilizing any suitable driving unit such as, forexample, a motor 81. The motor 8! drives the capstan I! through a shaft89, gears 9I and shaft 93, and it drives the twisting unit 8I throughshaft 95, adjustable reduction gears 91, shaft 99 and gears IIII. Acontroller I03 is provided to control the acceleration of the motor 81.

The operation of the tension control units II is similar to thathereinabove described with reference to Fig. 1 except that thecentrifugal devices GI have been omitted and the energization of thetorque motors 35 and field windings 21 of elec- 75 tric brakes I9 arecontrolled simultaneously by means of the electromagnetic device 31.

When switch 63 is closed, the torque motors 35 become energized andtension is thus applied to the strands I5. Arm I of controller I03 isadvanced in a clockwise direction to energize and accelerate the motor81. Thus the strands I5 are advanced and the twisting unit BI is rotatedto intertwist the strands. Assuming constant effective radius of thereel during acceleration, this initial tension may be represented by acurve I06 (Fig. 4). When the arm I05 has been advanced until the motor81 reaches a predetermined speed, which may be substantially full speed,it completes a circuit through contact segment IN to energize operatingcoil 39 thus actuating electromagnetic device 31 thereby deenergizingtorque motors 35 and energizing field windings 2'! of electric brakesI9. A slight change in tension results from this transfer and it may berepresented by the change from curve I06 to curve 13. As shown by curveI3, substantially constant tension of strands I5 is then maintainedduring the normal running operation in the manner hereinabove described.

To stop the operation of the system, the arm I05 is returned to theposition shown in Fig. 5, thus opening the circuit to operating coil 39.Electric brake I9 becomes deenergized and torque motor 35 becomesenergized. Because of the decreased efiective radius of the reel, thetension of the strands may be represented generally by curve I09 if itis assumed that the effective radius is constant during deceleration.

I do not wish to be restricted to the specific structural details,arrangement of parts, or circuit connections herein set forth, asvarious other modifications may be effected without departing from thespirit and scope of my invention. I desire, therefore, that only suchlimitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. In a system for combining a plurality of strands, in combination, aplurality of strand supplying means, means for advancing the strands ata substantially constant linear speed, and means cooperativelyassociated with each strand supplying means for maintaining apredetermined tension in the strands, each of the said tensioning meanscomprising a dynamo electric machine having a relatively highly reactivesquirrel-cage rotor winding and a field winding,,

means for connecting the said field winding to a constant potentialsource of unidirectional current.

2. In a system for combining a plurality of strands, in combination, aplurality of strand supplying means, means for normally advancing thestrands at a constant linear speed, means for controlling the saidadvancing means, electric torque producing means cooperativelyassociated with each strand supplying means for maintaining apredetermined tension in the strands, each of the said torque producingmeans comprising an alternating current motor and a dynamo electricmachine having a relatively high reactance rotor winding and a fieldwinding, and means cooperatively associated with the control means forconnecting the said alternating current motor to asource of alternatingcurrent when the said advancing means advances the strands at a speedbelow a predetermined magnitude and for connecting the said fieldwinding of the dynamo electric machine to a source of constant potentialunidirectional current when the strands are being advanced at a speedabove the predetermined magnitude.

3. In combination, tensioning means for a material passing from a rollat a constant linear speed, comprising a dynamo electric machine drivenby said roll, said dynamo electric machine having a field winding and arelatively high reactance squirrel-cage rotor Winding, and means forconnecting the said field winding to a source of constant potentialunidirectional current.

4. Incombination with a roll having a supply of material Wound thereon,means for normally drawing the material from the roll at a constantlinear speed, of electric torque producing means cooperativelyassociated with said roll for maintaining tension in the said material,the said torque producing means comprising an alternating current motorand a dynamo electric machine having a high reactance rotor winding anda field winding, means for connecting the said alternating current motorto a source of alternating current when the speed of. said roll is belowa predetermined magnitude and for connecting the said field winding ofthe dynamo electric machine to a source of constant potentialunidirectional current when the speed of said roll is above apredetermined magnitude.

5. In combination, tensioning means for a material passing from a rollat a constant linear speed, comprising a dynamo-electric machine drivenby said roll and capable of automatically developing substantiallyconstant power as the efiective radius of the roll varies, saiddynamoelectric machine having a field winding and a relatively highreactance squirrel-cage rotor winding, and means for connecting the saidfield Winding to a source of constant potential unidirectional current.

6. In combination, tensioning means for a material passing from a roll,comprising a dynamoelectric machine driven by said roll and capable ofdeveloping substantially constant power as the effective diameter of theroll varies, said dynamoelectric machine having a field winding, analternating current torque motor mechanically coupled to the saiddynamo-electric machine, means for connecting the field winding of thedynamoelectric machine to a source of constant potential unidirectionalcurrent when the material is passing from the roll at a predeterminedlinear speed, and means for energizing the said torque motor from asource of alternating current when the material is passing from the rollat a linear speed below the predetermined magnitude.

'7. In combination, tensioning means for a material passing from a roll,comprising means for starting and stopping the operation of said roll, adynamo-electric machine driven by said roll and capable of developingsubstantially constant power as the effective diameter of the rollvaries when the linear speed of the material is substantially constant,means for rendering said dynamo-electric machine ineffective during thestarting and stopping of the roll, and means for applying asubstantially constant predetermined tension to the material when saiddynamo-electric machine is rendered ineffective.

8. In combination with a roll having a supply ofmaterial wound thereon,means for normally advancing the material from the roll at asubstantially constant linear speed, means for starting and stopping theoperation of the 'said advancing means, of electric torque producingmeans cooperatively associated with said roll for maintainingsubstantially constant tension in the said material, the said torqueproducing means comprising an alternating current motor and adynamo-electric machine having a relatively high reactance rotor windingand a field winding, means for connecting the said field winding to asource of constant potential unidirectional current during the startingoperation of the said advancing means, and means for energizing the saidalternating current motor when the said field winding is deenergized.

9. In combination with a roll from which a material is normally advancedat a predetermined constant linear speed, means including adynamoelectric machine having a field winding and a relatively highreactance squirrel-cage rotor winding, and capable oi developingconstant power as the effective diameter of the roll varies when thelinear speed of the material is constant, control means cooperativelyassociated with said roll for rendering the said dynamo-electric machineeffective to maintain substantially constant tension in the materialwhen the speed of the roll reaches a predetermined magnitude, and means,rendered effective by the said control means, for maintaining tension inthe material when the speed of the said roll is below a predeterminedmagnitude.

10. In combination with a roll having a supply of material woundthereon, means for normally advancing the material from the roll at asubstantially constant linear speed, means for starting and stopping theoperation of the said advancing means, of electric torque producingmeans cooperatively associated with said roll for maintainingsubstantially constant tension in the said material, the said torqueproducing means comprising an alternating current motor and adynamo-electric machine having a squirrel-cage rotor winding and a fieldwinding, means for connecting said field winding to a source of.constant potential unidirectional current a substantial time intervalafter the starting operation has been initiated, means for deenergizingthe said field winding after the stopping operation has been initiated,and means for energizing the said alternating current motor when thesaid field winding is deenergized.

